An alternating e.m.f. of angular frequency ω is applied across an inductance. The instantaneous power developed in the circuit has an angular frequency
Which of the following is discovered from the discharge tube experiment?
A crooks tube is an early experimental electrical discharge tube with partial vaccum,invented by English physicist William crooks. it only describes the motion of electron because it contains a non-equilibrium plasma of positively charged ions, electrons and neutral atoms which are constantly interacting.
An air capacitor of capacity C = 10 μF is connected to a constant voltage battery of 12 volt. Now the space between the plates is filled with a liquid of dielectric constant 5. The charge that flows now from battery to the capacitor is
C = 10 μF
Charge in capacitor q = CV
= 10 x 12
= 120 μC
On keeping liquid of dielectric constant5, capacity will becomes of 5 time.
∴ Charge q = 5 x 120
= 600 μC
A string can withstand a tension of 50 Newtons. The greatest speed at which a body of mass 250 gm can be whirled in a circle using 50 cm length of string is—
F = mv2/R
50 = 0.25 × V2/ 0.50
V = 10m/s
The number of dry cells, each of e.m.f. 1.5 volt and internal resistance 0.5 ohm that must be joined in series with a resistance of 20 ohm so as to send a current of 0.6 ampere through the circuit is
In L-C-R series A.C. circuit, the phase angle between current and voltage is
'n' conducting wires of same dimensions but having resistivities 1, 2, 3, .....n are connected in series. The equivalent resistivity of the combination is
Two coils have a mutual inductance 0.005 H. The current cahnges in the first coil according to equation I=I₀ sin ωt where I₀ = 10 A and ω = 100 π rad/sec. The maximum value of e.m.f. in second coil is
The electrostatic energy stored in a capacitor is
Which of the following have minimum wavelength?
Cosmic rays have high frequency. So minimum wavelength.
An electric dipole placed in a non-uniform electric field experiences
Radius of the earth is 6400 km. The radius of the orbit of a stationary satellite is about
The force of gravitation is
Cosnider the following statements
Assertion (A) : The radiation from the sun's surface varies as the fourth power of its absolute temperature
Reason (R) : Sun is not a black body
Of these statements
The assertion is true but the reasoning is false
The sun is not a black body
The interference occurs in which of the following waves?
An ideal gas has a volume of V at 2 atm pressure. Keeping the temprature of gas constant, its pressure is doubled. The volume of gas will become
A body takes 1 1/3 times as much time to slide down a rough inclined plane as it takes to slide down an identical but smooth inclined plane. If the angle of inclination of the inclined plane is 45o, the coefficient of friction is
Consider l be the length of both the inclined planes and θ be the inclination. Then the times taken by a body sliding the smooth and rough inclined planes are
A current of 2 ampere flows in a long, straight wire of radius 2mm. The intensity of magnetic field at the axis of the wire is
A proton and an α-particle, moving with the same velocity enter into uniform magnetic field, acting normal to the plane of their motion. The ratio of the radii of the circular paths described by the proton and α-particle is
A cyclotron can not accelerate
Cyclotron is device used to accelerate charged particles. Cyclotron works on the principle that a charged particle moving normal to a magnetic field experiences magnetic lorentz force due to which the particle moves in a circular path and hence accelerates it.
Since a Neutron is neutral by charge. So, a cyclotron cannot accelerate it.
Plus, due to net zero charge on a neutron, it cannot be so easily accelerated by any method.
Magnetic moment of a magnet is M. Maximum value of torque acting on this magnet when suspended in a uniform magnetic field of intensity B is
A bar magnet of magnetic moment 100 units is cut into two halves of equal length, each half will have a magnetic moment of
Mag. moment = m×l since length is halved magneti... morec moment is also halved so it becomes 50units.
The magnetic susceptibility does not depend upon the temperature in
If the radius of a soap bubble is four times that of another, then the ratio of their pressures will be
Which of the following affets the elasticity of a substance?
All the factors change in temperature, hammering and annealing and impurity in substance affect the elasticity of a substance.
A column of water 60cm high supports a column of an unknown liquid of density 1500 kg m-3. The height of liquid column is (Density of water = 1000 kg m-3)
We equate pot. energy as itll be same for both the columns h1× density1 × g = h2 × dens. 2 × g 60 = 1.5 × h h = 40cm.
The moment of inertia of a meter scale of mass 0.6kg about an axis perpendicular to the scale and located at the 20cm position on the scale in kg m2 is (Breadth of the scale is negligible)
A rocket is fired upward from the earth's surface such that it creates an acceleration of 19.6 m/sec2. If after 5 sec its engine is switched off, the maximum height of the rocket from the earth's surface would be
Given a = 19.6 m/s2 = 2g
Resultant velocity of the rocket after 5 sec , v = 2g×5 = 10g m/s
Height achieved after 5 sec, h1
On switching off the engine it goes up to height h2 where its velocity becomes zero.
∴ Total height of rocket = 245 + 490 = 735 m
If a bullet of mass 5gm moving with velocity 100 m/sec, penetrates the wooden block upto 6cm. Then the average force imposed by the bullet on the block is
Equation of motion
v2 = u2 + 2as
2as = v2 - u2
2 x a x (6/100) = 0 - (100)2
12a / 100 = - 10000
a = -1000000 / 12 m/s2
This is the average retardation of the bullet
Avg force F = ma
= (5/1000) x 1000000 / 12 = 416.66 N
approx 417 newton
α - particle is equivalent to
It consists of two neutrons and two protons, and is thus identical to the nucleus of a helium atom. The rest mass of the alpha particle amounts to 6.64424.
If M(A;Z), Mp and Mn denote the masses of the nucleus AZX , proton and neutron respectively in units of u (1u=931.5 MeV/C2) and BE represents its bonding energy in MeV, then
Photons of energy of 6 eV are incident on a metal surface whose work function is 4 eV. The minimum kinetic energy of the emitted photoelectrons will be
Minimum kinetic energy is always zero.
The image formed by an objective lens of a compound microscope is
The image formed by objective lens of compound microscope is real and enlarged, while final image formed by compound microscope is inverted, virtual, enlarged and at a distance D to infinite or from an eye, on same side of eye piece.
Two identical pendulums are oscillating with amplitudes 2cm and 6cm. The ratio of their energies of oscillation will be
The work function of a metal is 4.2 eV. its threshold wavelength will be
An aeroplane is flying at a constant horizontal velocity of 600 km/hr at an elevation of 6 km towards a point directly above the target on the earth's surface. At an appropriate time, the pilot releases a ball so that it strikes the target at the earth. The ball will appear to be falling
The pilot will see the ball falling in straight line because the reference frame is moving with the same horizontal velocity but the observer at rest will see the ball falling in parabolic path.
The refracting angle of a prism A is small. The correct statement for the dispersive power of a prism is that dispersive power
A beam of white light passing through a prism is split up into its constituent colours. The light which undergoes least deviation is
A fish is swimming at a depth 2 m inside a lake of saline water. If refractive index of water is 1.25, then the radius of the circular aperture through which the fish sees the outside world, is
Which of the following forms a perfect image free from all aberrations?
Aberrations is a fact, an action or a way of behaving that is not typical, and that may be unacceptable. So present in spherical lens, cylendrical lens and spherical mirror. But plane mirror is free to aberration because it's have infinite focus length.
A thin uniform circular ring is rolling down an inclined plane of inclination 300 without slipping. Its linear acceleration along the inclined plane will be
Acceleration on an inclined plane
a= g sinθ/ (1 + I/MR2)
for circular rings: I= MR2
so by putting the value in above equation we get
a = g sinθ/ 2
a = g sin30/2
a = g/4
A simple pendulum consisting of a ball of mass m tied to a spring of length l is made to swing on a circular arc of angle θ in a vertical plane. At the end of this arc, another ball of mass m is placed at rest. The momentum transferred to this ball at rest by the swinging ball is
No momentum will be transferred because, at extreme position the velocity of bob is zero.
Indium impurity in germanium makes
Indium is trivalent, hence on doping with it, the intrinsic semiconductor becomes P-type semiconductor.
The general equation of S.H.M. is
N-type semiconductor is prepared by doping silicon semiconductor by a
The velocity of sound in air depends on
The speed varies depending on atmospheric conditions; the most important factor is the temperature.
Soap helps in cleaning clothes, because
Due to surface tension, liquids tend to minimize their surface area. Soap helps to lower the surface tension of solution, thus soap get stick to the dust particles and grease and these are removed by action of water.
The resistance of a heater coil is 110 ohm. A resistance R is connected in parallel with it and the combination is joined in series with a resistance of 11 ohm to a 220 volt main line. The heater operates with a power of 110 watt. The value of R in ohm is
Power consumed by heater is 110 W so by using P=
Also from figure
So i2 = 10 − 1 = 9A
Applying Ohms law for resistance R, V = iR
⇒ 110 = 9 × RÞ
If two bulbs of wattage 25 and 30, each rated at 220 volts, are connected in series with a 440 volt supply, which bulb will fuse
Safe current through 25W bulb =
Safe current through 30W bulb =
Now R1 = V2/P1 =
R2 = = 1613.3Ω
This is greater than the safe current for 25W bulb so, it well fuse
Two wire with resistances R and 2R are connected in parallel, the ratio of heat generated in 2R and R is
In a series circuit, the current is same across each resistor.
So, energy developed in resistors is : I2Rt
thus the ratio is : R1/R2 = 1/2
A 2m long Aluminium pipe at 27oC is heated until it is 2.0024m at 77oC. The coefficient of linear expansion of aluminium is
∆l= L c ∆T (here c is coefficient of linear expansion, ∆l is change in length, L is previous length and ∆T is change in temperature ) 0.0024 = 2 × c × 50c = 24× 10–6 °C
So (a) should be answer.
A reversible engine converts one-sixth of the heat into work. When temperature of sink is reduced by 62oC, the efficiency of the engine is doubled. The temperature of source and sink are
Maximum efficiency of an engine working between temperatures T2 and T1 is given by the fraction of the heat absorbed by an engine which can be converted into work is known as efficiency of the heat engine.
6T2 - 6T1 = T2
Therefore, T2 = 1.2 T1 .....(1)
Where T2 is the source temperature and T1 is the sink temperature.
If the sink temperature (T1) is reduced by 62oC, the efficiency gets doubled i.e.
6T2 – 6T1 + 372 = 2T2
6T2 – 2T2 – 6T1 + 372 = 0
4T2 – 6T1 + 372 = 0
Substituting the value of T2 from equation (1), we will get,
4(1.2 T1) – 6T1 + 372 = 0
4.8 T1 – 6T1 + 372 = 0
372 = 1.2 T1
T1 = 310 K = 37oC
Therefore, T2 = 1.2 x 310 = 372 K = 99oC
Hence, temperature of the source and the sink is 99oC and 37oCrespectively.
Which type of thermodynamic process is heating of water at atmospheric pressure?
Light year is a unit of
A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km.
The unit of reactance is
Reactance is mathematically symbolized by the letter “X” and is measured in the unit of ohms (Ω).
The penetration of light into the region of geometrical shadow is called
Which of the following property of light waves is not observed in sound waves?
Two adjacent piano keys are struck simultaneously. The notes emitted by them have frequencies n₁ and n₂. The number of beats heard per second is
The path difference between two waves γ₁ = a₁ sin (ωt - 2πx/λ) and γ₂ = a₂ cos (ωt - 2πx/λ + φ) is
The power of a pump, which can pump 200 kg of water to a height of 200 m in 10s is (Take g=10 ms-2)
Mass of water : m=200 kg
Height upto which the water is raised : h=200 m
Work done : W=mgh=200×10×200=400000 J
Power of the pump :